Not Applicable.
1. Field of the Invention
The invention relates to methods and devices for air-to-ground target detection, acquisition and terminal guidance, and is directed more particularly to methods and devices for correlating selected prepared imagery with imagery produced by an airborne platform-mounted sensor, to obtain improved guidance of air-launched weapons to a selected target designated on the prepared imagery.
2. Description of the Prior Art
It is known to use multispectral image correlation systems in air-to-ground target detection and acquisition. Such systems include means for image-processing, which automatically register images produced by airborne platform-mounted sensors operating in different wavelengths and from different points of view.
There is a need for an improved, more accurate guidance system which can be used in conjunction with airborne platform-mounted sensors and additionally, for precision terminal guidance of weapons with imaging sensors thereon.
An object of the invention is, therefore, to provide a method for providing improved accuracy in guidance systems for air-launched weapons, such as air-to-ground missiles.
A further object of the invention is to provide a multispectral gradient based image correlation system for use in carrying out the above method.
A still further object of the invention is to provide such an image correlation system suitable for other uses wherein a current real-time image is compared with a recorded image.
With the above and other objects in view, as will herewith appear, a feature of the present invention is the provision of a method for enhancing air-to-ground target detection, acquisition, and terminal guidance, the method comprising the steps of:
(1) providing a reference image of a target scene with a designated selected target therein,
(2) detecting contrast boundaries and orientation thereof in the reference image,
(3) identifying maxima edge pixels in the reference image determined by contrast boundaries, and tracing edges along the maxima edge pixels,
(4) converting points in the reference image to points in three-dimensional space, and compressing the reference image by fitting straight line segments to the reference image edges, and storing in a computer memory only end points of the straight line segments, which constitute a reference image template,
(5) providing a video image of the target scene from a sensor mounted on an airborne platform,
(6) identifying contrast boundary edges of the video image;
(7) transforming and scaling the template to a line-of-sight, range, and field-of-view of the sensor,
(8) correlating the edges of the video image with the transformed and scaled template made from the edges of the reference image, and
(9) converting the selected target designation in the reference image to the sensor image.
In accordance with a further feature of the invention, there is provided a multispectral gradient based image correlation system comprising a template containing information as to edges in imagery of a target scene, and a selected target therein, a video image of the target scene produced by sensor imagery and processed by a gradient operator into a gradient based edge image, means for transforming, scaling and correlating the template image with the gradient based edge image, and means for transferring the selected target from the template to the gradient based edge image, whereby to place the selected target in the video image which is correlated edge-to-edge with the template target scene imagery.
In accordance with a still further feature of the invention, there is provided a multispectral gradient based image correlation system comprising a template containing information as to edges in recorded and stored imagery depicting a reference item, a video image processed by a gradient operator into a gradient based edge image, and a means for correlating the template imagery with the gradient based edge image.
The above and other features of the invention, including various novel details of method steps, arrangements, and combinations of parts, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method steps and devices embodying the invention are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.